Norman invasion of Ireland

The Norman invasion of Ireland occurred from 1169 to 1175 when the Anglo-Norman barons of England invaded Ireland under the pretense of aiding the deposed King of Leinster. The success of the Norman mercenaries led to King Henry II of England involving himself in their campaigns and conquering much of the island, establishing the Lordship of Ireland and initiating 750 years of English rule over Ireland.

Background
The death of Brian Boru at the Battle of Clontarf in 1014 ushered in a period when rival Irish kings fought for power. The most powerful Irish ruler from 1086 to 1114 was Muirchertach O'Brien, who began to develop relations with the Normans in Britain. He was supplanted by Turlough O'Connor (1106-56), who built a series of castles around Connacht and destroyed the power of Munster. He commissioned the Cross of Cong to hold a relic of the True Cross.

History
A rivalry over the lordship of Dublin brought about the English invasion of Ireland in 1171. Dermot MacMurrough, King of Leinster, claimed to be King of Dublin, but he was unpopular there. Rory O'Connor, King of Connaught, took advantage of this in 1166 to send his ally, Tighearnan O'Ruairc, against MacMurrough. Driven into heavily wooded territory around Ferns, County Wexford, the Leinster king was unable to rally support and took ship for Bristol.

MacMurrough travelled to Aquitaine in France to offer homage to King Henry II of England in the hope of securing the English king's assistance. But Henry, caught up in a quarrel over his Archbishop of Canterbury, Thomas Becket, was in no mood to take on a costly campaign in Ireland. Rebuffed, Dermot turned to other ambitious members of the Anglo-Norman minor nobility.

Norman power
The effect on the MacMurrough cause was electrifying. The Norman force that answered Dermot's call took Wexford within two days. MacMurrough handed the city over to his allies in return for their acknowledging him as their overlord. The allies endured a few difficult moments in 1169, as the Leinster King's enemies, Domnall Mac Gilla Patraic of Osraige and the High King Rory O'Connor, tried to combine their forces to crush him, but in August 1170 they were reinforced by MacMurrough's most powerful Norman ally, Richard fitzGilbert de Clare, Earl of Pembroke (nicknamed "Strongbow"). The new arrivals soon took Waterford, drove out Askulv, the Viking lord of Dublin, and took possession of the city.

Henry's arrival
The astonishing success of such a comparatively small group of Norman knights finally attracted the attention of Henry II. The English king's landing at Waterford had, in theory, papal sanction, for in 1156, Pope Adrian IV (the only English Pope) had granted a papal bull Laudabiliter giving Henry permission to invade Ireland. Although this may have been a pretext, Henry was probably in reality more concerned with gaining control of the large lands his notional vassals were carving out for themselves in Ireland. Henry regularized the situation by appointing his own man, Hugh de Lacy, as Constable of Dublin and placing garrisons loyal to him in key towns such as Cork and Limerick. Although Henry returned to England in spring 1172, de Lacy and Strongbow continued to build up their holdings in the face of sporadic Irish resistance. In 1175, Rory O'Connor acknowledged that the English could not be expelled and agreed the Treaty of Windsor with Henry II, by which he was recognized as High King in the western part of Ireland, although he was to pay a tribute to the English King, while the eastern portion, including Leinster, Meath, Waterford, and Dublin was to remain in the hands of the Anglo-Norman barons.

English possession
Neither the barons nor the other Irish kings paid much attention to the treaty, and warfare continued between them. The death of STrongbow in 1176 brought a greater involvement by the English Crown and in 1183, Henry II had his son Prince John crowned as King of all Ireland following the death of Rory O'Connor.

With the English in possession of the east and north of Ireland, colonization from England over the next few centuries changed the character of the area to resemble the feudal lordships on the other side of the Irish Sea. The English-controlled area (known as the Pale of Settlement) gradually expanded with the conquest of most of Connaught by 1235. Royal control, meanwhile, strengthened as the liberties of the barons were restricted. By 1300, the remaining Irish kings ruled reduced domains and were the feudal tenants of English barons.

Aftermath
The native Irish kingdoms experienced a resurgence in the 14th century, but subsequent invasions from Scotland and England again crushed their power. The invasion by the Scottish king Robert Bruce's brother Edward in 1315 destabilized the English position, but control was re-established. When Irish dissident threatened to turn to rebellion, the English response could be brutal, as during the Nine Years' War (1594-1603) and Cromwell's campaign. King John appointed a chamberlain of the exchequer in 1215 to administer royal revenues. A Court of the Exchequer was established in the reign of Henry III of England to adjudicate on fiscal matters.